The kiss activates 35 muscles, accelerates the heart from 70 to 120 beats per minute, dilates blood vessels and pupils, triggers oxytocin, dopamine and endorphins, lowers cortisol (the stress hormone).
The ancient Romans had three terms to distinguish this gesture: Osculum, social kiss, friendly or respectful; Basium, between family but also sometimes erotic; Savium, sexual or erotic.